Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered without help from the description. The description adds one genuinely useful behavioral fact beyond that: the result is scoped to the currently loaded avatar, making it state-dependent. It says nothing about what happens if no avatar is loaded or whether the result is paginated.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single sentence with the resource and scope front-loaded and the downstream purpose appended. Every clause earns its place, with no redundant restatement of the title.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a no-parameter, read-only discovery tool with annotations covering safety and no output schema, the description covers what it returns (expression and animation names) and why (to trigger one by name). The one notable omission is the prerequisite that an avatar must be loaded, which matters given the "currently loaded avatar" scoping.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes no parameters, so there is no parameter meaning to explain and the baseline of 4 applies. The description correctly implies the only scoping input is implicit state (the loaded avatar) rather than an argument.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ("List the expressions and animations") scoped to "the currently loaded avatar", which is more precise than the generic title. It does not explicitly name a sibling, but the phrase "so one can be triggered by name" signals the natural downstream tool (play_action), making the intent distinguishable in practice.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The clause "so one can be triggered by name" conveys the intended use in context: call this first to discover valid action names before triggering one. No exclusions or named alternatives are given, and no prerequisites (e.g., an avatar must be loaded) are stated, so it falls short of a full when/when-not treatment.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.